1. Field of the Invention
The present invention relates to the field of image processing. More specifically, the present invention relates to a method and apparatus for automatically adjusting the rate at which a bit stream is processed.
2. Description of the Related Art
This technique is suitable for widely-used image compression standards that integrate various algorithms into a compression system. Such image compression standards include video compression standards, such as the digital video standards specified by the Motion Picture Experts Group (the MPEG standards), by the Join Photographic Experts Group (the Motion JPEG standard), and by the Digital VCR Conference (the xe2x80x9cBlue Bookxe2x80x9d or DV standard), all of which standards are included herein by reference.
The MPEG, JPEG, and DV standards are distinct compression formats based on discrete cosine transform (DCT) technology. The MPEG (in particular, MPEG-2) standard is currently popular as a distribution format for satellite, cable, terrestrial broadcasting and digital video disc (DVD). The MPEG format uses a compression algorithm that utilizes both intraframe and interframe compression. The JPEG standard is most popularly used as a format for still images, but it may also be applied to video (Motion JPEG). The JPEG format uses only intraframe compression. The DV standard is currently gaining popularity as acquisition format for consumer digital camcorders, as well as professional digital cameras and post-production editing systems. Like the JPEG format, the DV format uses only intraframe compression.
The intraframe compression or encoding process in accordance with the above standards typically proceeds according to the process shown in FIG. 1. FIG. 1 is a flow diagram showing a conventional digital image encoding process (100). In a first step (102), the encoder constructs Nxc3x97N (typically 8xc3x978) blocks from a digital image input into the encoder. The result is a matrix of image blocks i(n1,n2), where n1,=1,2,3, . . . , N1; n2=1,2,3, . . . , N2; N1,=the number of rows; and N2 =the number of columns. In a second step (104), the encoder applies a forward transform (typically a cosine related transform) to the matrix of image blocks to generate a matrix of transformed blocks I(k1,k2). In a third step (106), the encoder divides the matrix of transformed blocks I(k1,k2) by a predetermined, fixed quantization table or matrix Q(k1,k2), and subsequently quantizes the result to produce a quantized transformed matrix S(k1,k2) which comprises a matrix of symbols. Finally, in a fourth step (108), the encoder applies symbol encoding to transform the matrix of symbols S(k1,k2) to an output bit stream.
FIG. 3 is a flow diagram showing a conventional digital image decoding process (300). In a first step (302), the decoder receives an input bit stream and applies symbol decoding to regenerate the symbol matrix representing the quantized transformed matrix S(k1,k2). In a second step (304), the decoder multiplies the symbol matrix S(k1,k2) by the same predetermined, fixed quantization matrix Q(k1,k2) to produce a transformed matirx Ixe2x80x2(k1,k2). This transformed matrix Ixe2x80x2(k1,k2) is an approximation of the original transformed matrix I(k1,k2), some fidelity having been permanently lost due to the quantization step (106) of the encoding process (100). In a third step (306), an inverse transform is applied to generate an image block matrix ixe2x80x2(n1,n2). The image block matrix ixe2x80x2(n1,n2) is an approximation of the original image block matrix i(n1,n2). Finally, in a fourth step (308), the blocks are merged to form an output digital image which is an approximation of the original image.
The present invention provides new and improved apparatus and methods for encoding and decoding of a series of digital images. The throughput bit rate of conventional systems varies depending upon the complexity of the images. Applying apparatus and methods of the present invention, encoding and decoding of a series of digital images may be adjusted in an automated manner to achieve a constant throughput bit rate.
For further understanding of the nature and advantages of the present invention, together with other embodiments, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.